Solid lubricant, which is used for embedding in a sliding surface of a sliding member substrate of copper alloy or the like, gives a sliding effect by forming as solid lubricant film on the sliding surface. Thus, quality of the solid lubricant film largely affects friction coefficient, abrasion resistance, and film lifetime.
Among such type of solid lubricants, are solid lubricants having layered structure, particularly solid lubricants whose main component is graphite. Due to its layered structure, graphite shows high resistance in the load direction and shows low resistance in the sliding direction. Further graphite is soft, and has the property of being able to keep lubricating performance in a wide range of temperatures between ordinary temperature and a high temperature.
However, graphite-based solid lubricants are somewhat lacking in film-forming ability, and have inadequate film lifetime against repeated friction. Accordingly, graphite-based solid lubricants are restricted in conditions of use for sliding member, and are not suitable, for example, for use under high load.
As solid lubricants usable in high-load applications, can be mentioned solid lubricants composed of tetrafluoroethylene resin, soft metals such as indium, lead and tin, and wax. For example, there is a solid lubricant comprising tetrafluoroethylene resin, lead, polyolefin resin, and some kind of wax. This solid lubricant has a very low friction coefficient under high load condition, is superior in film-forming ability, and has long film lifetime and superior self-repairing property of film.
The solid lubricant comprising tetrafluoroethylene resin, lead, polyolefin resin, and some kind of wax provides superior sliding performance as described above. However, this solid lubricant is unfavorable since it contains lead, an environmental burden substance.
On the other hand, as a solid lubricant containing no lead as its constituent, there are known a solid lubricant (Patent Literature 1) formed of synthetic resin containing melamine-isocyanuric acid adduct, and a solid lubricant (Patent Literature 2) composed of polyethylene resin, hydrocarbon-based wax, and melamine cyanurate.